Sonic The Hedgehog Prototype Dumped Online

One of the biggest events in the history of video game history has taken place as a prototype of the original Sonic the Hedgehog on the Sega Genesis/Mega Drive has been found and dumped online for all to enjoy.

Available via Hidden Palace, the file has already been downloaded and played numerous times on its first day (January 1, 2021) with a laundry list of differences already found between the prototype and the final version.

You can view a list of differences currently known and a 1 hour video of the prototype in action down below:

General differences:

• The ROM header hasn’t been populated with game specific information yet.
• The prototype uses a standard SEGA title screen commonly used in other games. The SEGA scream is absent and isn’t present in the ROM.
• The “Sonic Team Presents” screen is completely absent.
• The title screen lacks a trademark symbol.
• The title screen has a “PRESS START BUTTON” prompt. This is absent in the final version, even though it’s still present in the game’s code.
• Sonic’s palette on the title screen is slightly brighter in comparison to the final build.
• Level select can be activated by pressing A+START on the title screen. For the final version, a level select code is used instead (UP, DOWN, LEFT, RIGHT, A+START). There is no code for a level select cheat. Debug mode can still be entered by holding A button while selecting a level from the level select.
• The original level names for Spring Yard Zone and Scrap Brain Zone are still present in the level select.
• A cross was added next to all of Star Light Zone and Act 3 of Clock Work Zone, despite Star Light Zone being accessible. This seems to be a left over from when Star Light Zone wasn’t accessible from the level select yet.
• Final Zone is missing from the level select.
• Clock Work Zone Act 3, Final Zone, and the ending level have not been implemented yet.
• The staff credit sequence, continue screen, and the ending sequence have not been implemented and do not exist in the ROM in any form yet.
• Pressing B on any of the levels in the level select loads up a strange version of Green Hill Zone Act 3. This is technically an “Act 4” for Green Hill Zone, and was most likely a way to test the ending area used before the end credits in the final game.
• The title card used for each level has “ACT .” instead of “ACT”.
• The demo after the title screen desyncs, causing Sonic to die instantly. It seems that the demo was recorded for a different level layout. The same demo recording seems to be used for each level presented. The game uses a different fade out routine when Sonic dies during a demo.
• The level order consists of Green Hill Zone (Acts 1, 2, 3), Marble Zone (Acts 1, 2, 3), Sparkling Zone (Act 1), and Star Light Zone (Act 1). This suggests that the final level order has been decided at this point. The levels presented are all the acts that have been finished to a point where they could be completed. The game resets back to the SEGA logo after completing Star Light Zone Act 1.
• Each level contains significant level layout differences, with Green Hill Zone and Marble Zone containing the least and Star Light, Labyrinth, Sparkling, and Clock Work containing the most..
• Sonic’s tile set lacks his final sprite for picking up an air bubble and an additional fall back animation frame. All other sprites are identical.

Gameplay differences:

• The HUD says RING instead of RINGS.
• The HUD does not flash red when Sonic’s RING count is at zero, or when time is running out on the clock.
• Continues haven’t been implemented yet.
• Lives can be received after receiving 50 rings. In the final, you must collect 100 rings to receive an extra life.
• You can go back to the title screen at any time by pressing START + A.
• The music doesn’t stop when the game is paused.
• End level bonus points have not been implemented. Instead, Sonic leaps into the air after an act is complete.
• It isn’t possible to enter a special stage while in a level yet.
• None of the levels contain signposts.
• Time over has not been implemented. The timer resets to 9:00 if it reaches past 9:59.
• Big rings that lead to special stages have not been implemented completely yet, but code and art for it exists in the ROM.
• The vertical movement for the camera is slower than the horizontal, causing Sonic to often out run the camera when falling down. In levels with death pits, this can cause Sonic to die mid air.
• Points received from enemies and certain objects do not multiply when received in succession. You will only receive 100 points from each badnik you destroy.
• The boss in Green Hill Zone is the only boss in the game.
• The game recognizes the button to jump before activating debug mode with the same button. This causes Sonic to jump after exiting debug mode. This was fixed for the final version.

Green Hill Zone differences:

• The level contains a rolling ball hazard that goes unused in the final game. The rolling ball itself is modeled after Robotnik’s wrecking ball that’s used for the boss in this level. If Sonic moves over the ball or moves against it, the ball will chase after him. If the ball rests on a cliff, it will move in Sonic’s direction even if Sonic runs underneath it. If the ball falls on top of Sonic, it will crush him to death. If the ball hits Sonic as it’s rolling on the same platform as Sonic however, it will only push him (it doesn’t hurt to the touch). This causes bugs where the ball can clip Sonic through level collision. The ball itself can map to most level collisions, and even carries its own momentum when it goes down hill, allowing it to move up half pipes and hills. However, it does not recognize the path swap flags, so it cannot go around loop de loops. Despite reports to the contrary in the media when the game was in development, the ball in its current state cannot destroy badniks or break down walls. The ball cannot be controlled if Sonic is on top of it. However, the ball does seem to react to when Sonic’s on top of it. However, it seems to cause the ball to lose its ability to recognize level collision.
• The background art is slightly different. Each Act contains a slightly different background.
• Rotating flowers are pink. In the final they are green.
• Green Newtron badniks are pink in this build.
• Platforms float at the same time and at the same rate of speed.
• The rotating light underneath Robotnik’s ship doesn’t flash in the prototype.
• When Robotnik has been defeated, he flies away much faster.
• The boss music keeps playing even after Robotnik has been defeated.

Labyrinth Zone differences:

• This stage contains a completely different static background in comparison to the final version. The prototype takes place under an open cave with light shafts. In the final, the level takes place in an area with mostly ruins and architecture.
• This stage completely lacks water and bubbles. It appears that water has barely been programmed in the game yet.
• This stage is completely devoid of objects and badniks in any act. However, art and code for the Jaws and Burrobot badniks exist in the game’s object table, but go unreferenced.
• The stage’s debug object list only contains a ring, an item box, and a broken version of the Crabmeat badnik.
• Sonic doesn’t die if he falls into a bottomless pit. Instead he just warps to the top of the stage.
• The statue that pours water that Sonic would normally slide down on is bigger in the prototype.
• The stage lacks a boss.

Marble Zone differences:

• The level background contains UFOs that animate in the sky all throughout the level. This was removed from the final.
• This level contains the Spikes badnik instead of the Caterkiller badnik. Caterkiller doesn’t seem to exist in the ROM yet.
• Inside the debug mode’s object list is the Splats badnik, which was cut from the final (only the art remains in the final version).
• There is a gimmick that goes unused for the final where Sonic has to repeatedly jump on a crushing platform to reach the other side. This was replaced by a platform that can be lowered with a switch.
• If Sonic dies around lava, the debug markers that are used to indicate where the object that causes Sonic to get hurt when he touches lava appears. This occurs even if debug mode isn’t actually enabled.
• You don’t earn points when breaking blocks.
• There is no boss in Act 3. Instead there is a sign post shortly before the boss arena.
• There is a bug in Act 3 that causes the game to lock the camera in place when Sonic is in a specific spot underneath the area where the end level sign post was added.

Star Light Zone differences:

• The background art is slightly different.
• Sonic suffers from some collision issues when going down half pipes and slopes, oftentimes slowing or stopping even though there is nothing in front of him.
• The loop de loops contain lights on the top.
• Seesaws exist in the debug object list but go unused. While the seesaws function, they lack the spike ball that helps propel Sonic into the air.
• The stage is more difficult overall in comparison to the final build, containing more opportunities for Sonic to fall into a bottomless pit.
• There are no badniks in any acts for this zone. Bomb badniks have not been added yet.
• Marble Zone’s spitting lava object is on the debug object for this zone for some reason.
• Act 2 and 3 are almost completely devoid of objects, but there are some objects placed in strange places.
• The sign post that was added to the end of Act 1 is further down into the ground in this build.
• The game resets back to the SEGA screen after the end of Act 1.
• The stage lacks a boss.

Spring Yard Zone (Sparkling Zone) differences:

• The background is completely different in comparison to the final. The background utilizes a flashing, neon colored palette for background billboards and stars set at night. In the final build, the stage is set to city outskirts during the evening/twilight.
• The Roller badnik is present in the object list and is completely functional, but goes unused.
• Act 2’s object layout was in the middle of being implemented at the time of this build, as the beginning of the zone contains objects but gets progressively more barren as the act goes on.
• Act 3 is completely devoid of any objects.
• You don’t earn points from hitting bumpers.
• The stage lacks a boss.

Scrap Brain (Clock Work Zone) differences:

• In the prototype, Scrap Brain Zone is referred to as Clock Work Zone.
• The title card for this stage reads “CLOCK ORK ZONE” instead of “CLOCK WORK ZONE”. This is because the art for the “W” does not exist.
• The background in Act 1 is completely different in comparison to the final version. Act 1 is actually using Act 2’s foreground as part of the background.
• Act 2 lacks any background.
• All acts are completely devoid of objects.
• The foreground art contains various different tiles in comparison to the final version.
• The object list for this zone contains just a ring, a monitor, and a broken copy of the Crabmeat badnik. However, there is unreferenced data that suggests that the Ball Hog badnik was planned for this zone already. The Ball Hog object is based on its original front facing design, and can still be restored and loaded with all of its art and code in the ROM.
• Act 2 contains smaller rotating circles which were removed from the final build.
• The zone contains slanted non working conveyor belts which go unused in the final build.
• None of the acts can be completed.
• Act 3 hasn’t been started yet.
• The stage lacks a boss.
• Death pits haven’t been added yet. If Sonic falls down, he warps to the top of the level.

Special Stage differences:

• The unique level fade in and out does not exist in the prototype. Instead, the normal level fade in and out is used.
• Uses just one level layout, which looks nothing like any of the layouts used in the final version. It doesn’t appear that other layouts exist in the ROM.
• Debug mode cannot be activated for the Special Stage.
• The Goal spheres do not cause Sonic to exit the Special Stage.
• Touching the line of red spheres ends the Special Stage. The arena rotates exponentially before suddenly coming to a stop. After a few seconds, Sonic warps back to the starting point.
• The rotation can be controlled by pressing A and B, each button slowly increases the speed in the opposite direction.
• Only rings, bumpers, and spheres that control the rotation direction exist in the stage, there are no emeralds to collect and the squares that disappear to the touch haven’t been implemented yet. Graphics for the emeralds do exist in the ROM, however.
• The completion screen hasn’t been implemented yet.
• Special Stages do not use a unique animation when entered, the A and B buttons also cannot be used to jump, and object placement mode cannot be entered. A and B speed up/slow down the stage’s rotation and pressing START will reset the rotation speed to 0.

Music and Sound differences:

• The sound sample used for the drum snare sounds different. It’s a higher quality version of the drum snare used for the final build.
• There are some audio glitches near the end of the 1UP sound cue. This can sometimes cause other audio problems to occur in the sound driver.
• Track $92 in the sound test crashes the game. This is caused by an invalid pointer.
• The credits medley contains some different instrument programming.
• The ending BGM has a slightly different ending.
• The drowning BGM and emerald collect sound cues do not exist yet.
• The SEGA scream does not exist on the sound test